The conventional design for a scroll compressor usually includes a stationary scroll plate and a driven scroll plate disposed in parallel, facing arrangement, each plate having involute wrap elements attached in intermeshed, fixed angular relationship. The driven plate is caused to move in an orbital path relative to the stationary plate so that pockets of fluid defined by flank surfaces of the wrap elements move between an inlet adjacent the radially outer ends of the wrap elements and an outlet adjacent the axial center of the wrap elements.
The conventional scroll compressor has an outlet opening in the stationary scroll plate through which compressed fluid is discharged, either into an enclosed volume, or directly into a tube leading to an external discharge port. If the scroll compressor is housed within a hermetic shell, the volume enclosed by the shell may be at suction pressure, discharge pressure, or split into two parts, one at suction and the other at discharge pressure. Examples of each configuration are shown in U.S. Pat. Nos. 4,389,171 and 4,365,941, and Japanese Laid Open Patent Application No. 57-70984, respectively. Where the shell is at discharge pressure, suction fluid is delivered to the involute inlet either directly as shown in the '941 patent or via a tube that extends from the scroll plates to a suction port in the shell. If the shell is divided into two parts at different pressures, as disclosed in the above-cited Japanese Laid Open Application, compressed fluid is conveyed via a passage through the stationary scroll plate to the lower part of the shell enclosing the compressor drive shaft; the inlet to the radially outer ends of the involutes is in fluid communication with the upper part of the shell, i.e., with the volume that is at suction pressure.
The manufacturing costs of providing a radial discharge passage within the stationary scroll plate is prohibitive. A lower cost alternative would be to provide a discharge tube extending from a port in the center of the stationary plate over to the periphery of the scroll plates, and through the framework of the compressor to the volume comprising the lower part of the shell. The disadvantage of this approach is that the discharge tube would pass through the volume of fluid which is at suction pressure, resulting in undesirable heat transfer between the hot compressed fluid and the cooler suction gas.
The configuration selected for the scroll compressor can greatly affect the design of its lubrication system. For a scroll compressor enclosed in a shell at suction pressure, oil is usually pumped from a reservoir at the bottom of the shell through a bore in the drive shaft to bearings and other surfaces requiring lubrication. Centrifugal force developed by rotation of the drive shaft carries the oil up the bore to various lateral passages that direct lubricant to the bearings.
In a "high side compressor", the oil reservoir is exposed to discharge pressure. This pressure may be used to force oil through a small diameter delivery tube up to the involute inlet. At this point, the oil mixes with the fluid being compressed and is carried through the compression cycle. The oil improves the seal along the flanks and the tip surfaces of the involute wrap elements and reduces friction. However, oil must be separated from the compressed fluid before it is discharged from the compressor shell. Once separated, the oil should be used to lubricate other parts of the compressor before being allowed to flow back into the reservoir.
In consideration of the foregoing, it is an object of this invention to provide a split shell scroll compressor with both high efficiency and relatively low production costs.
It is a further object to minimize heat transfer between compressed fluid discharged from the scroll plates and suction fluid entering the compression cycle.
A still further object is to discharge compressed fluid directly through the orbiting scroll plate.
Yet a further object is to supply oil to the involutes to improve their sealing action and to reduce friction.
Moreover, it is an object of this invention to separate entrained oil from the compressed fluid as it is discharged from the scroll plates, and to cause the oil to lubricate adjacent bearing surfaces.
These and other objects of the invention will be apparent by reference to the attached drawings and to the description of the preferred embodiment that follows hereinbelow.